An imaging device such as a camera requires at least three things. First, a light sensitive medium is required. In the past, the light sensitive medium has been photographic film. Recently, however, photographic film has been increasingly been supplanted with two dimensional arrays of photodetectors.
The second thing required by a camera is a lens and enclosure for limiting the light impinging upon the light sensitive medium from unintended directions and for focusing an image from an image source onto the light sensitive medium. The lens may be either of a fixed focus design or variable focus to accommodate near or distant image sources.
The final thing required of a camera is a shutter to limit the time length of exposure of the image sensitive medium to light from the image source. In the case of photographic film, the control of the time of exposure is critical to forming a sharp image. If the shutter remained open too long, then the film would be overexposed and of little value. If the shutter open time was too short, then the film would be underexposed and also of little value.
The use of an array of photodiodes as a light sensitive material does not change the criticality of shutter open time. Once more, if the shutter is open too long, then the image formed within the array is overexposed. If the shutter is not open long enough, then the image is underexposed.
Prior art shutters typically include a light control device that physically moves into and out of a light path to expose the light sensitive medium and a timing device. The light control device is usually made of one or more metal leafs and a mechanism to quickly move the metal leafs between an open and closed position. The timer may also be mechanical or may be some sort of electrically activated device the moves the metal leafs between the open and closed positions.
While prior art mechanical shutters perform well under most situations, they tend to be relatively large, expensive to make and suffer from reliability problems. Accordingly, a need exists for a more reliable shutter for use with compact cameras.